1. Field of the Invention
The present invention relates to a resin-made floor panel structure applied to a floor of vehicle such as automobile.
2. Description of the Related Art
As is well known, conventionally, the floors of vehicles such as automobiles have been constituted by using floor panels made of steel.
Recently, however, for a higher fuel cost efficiency, for example, the car body is expected to reduce in weight progressively. And, in order to meet such need, it is attempted to reduce the weight of the vehicle floor by using a floor panel made of resin. For example, Japanese Patent Laid-open Publication No. 2001-10542 discloses a manufacturing method of automobile floor by expansion molding.
By using a resin-made floor panel instead of steel plate structure, the weight of the vehicle floor is reduced, but the strength and rigidity are lowered at the same time, and further due to weight reduction of panel itself, the resonance point becomes higher, and problems of vibration and noise in the floor section become more serious, as a result silent compartment is disturbed.
To solve such problems, it may be considered to increase the thickness of the resin floor panel, but if the thickness is increased too much, the weight and the manufacturing cost are increased, and the merit of using resin for floor panel may be lost.
When absorbing sound in a space, it is known that the sound energy density is higher as the space volume is smaller, and that the sound can be absorbed and attenuated more effectively. It is more advantageous when the air tightness of the space is higher. Therefore, to suppress transmission of floor section noise to the compartment side, it is important to absorb sound or isolate sound in a space of small volume and high degree of air tightness.